/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.mvc.condition;

import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.Set;

import javax.servlet.http.HttpServletRequest;

import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.cors.CorsUtils;

/**
 * A logical conjunction (' && ') request condition that matches a request against
 * a set of header expressions with syntax defined in {@link RequestMapping#headers()}.
 *
 * <p>Expressions passed to the constructor with header names 'Accept' or
 * 'Content-Type' are ignored. See {@link ConsumesRequestCondition} and
 * {@link ProducesRequestCondition} for those.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public final class HeadersRequestCondition extends AbstractRequestCondition<HeadersRequestCondition> {

    private final static HeadersRequestCondition PRE_FLIGHT_MATCH = new HeadersRequestCondition();


    private final Set<HeaderExpression> expressions;


    /**
     * Create a new instance from the given header expressions. Expressions with
     * header names 'Accept' or 'Content-Type' are ignored. See {@link ConsumesRequestCondition}
     * and {@link ProducesRequestCondition} for those.
     *
     * @param headers media type expressions with syntax defined in {@link RequestMapping#headers()};
     * if 0, the condition will match to every request
     */
    public HeadersRequestCondition(String... headers) {
        this(parseExpressions(headers));
    }

    private HeadersRequestCondition(Collection<HeaderExpression> conditions) {
        this.expressions = Collections.unmodifiableSet(new LinkedHashSet<>(conditions));
    }


    private static Collection<HeaderExpression> parseExpressions(String... headers) {
        Set<HeaderExpression> expressions = new LinkedHashSet<>();
        for (String header : headers) {
            HeaderExpression expr = new HeaderExpression(header);
            if ("Accept".equalsIgnoreCase(expr.name) || "Content-Type".equalsIgnoreCase(expr.name)) {
                continue;
            }
            expressions.add(expr);
        }
        return expressions;
    }

    /**
     * Return the contained request header expressions.
     */
    public Set<NameValueExpression<String>> getExpressions() {
        return new LinkedHashSet<>(this.expressions);
    }

    @Override
    protected Collection<HeaderExpression> getContent() {
        return this.expressions;
    }

    @Override
    protected String getToStringInfix() {
        return " && ";
    }

    /**
     * Returns a new instance with the union of the header expressions
     * from "this" and the "other" instance.
     */
    @Override
    public HeadersRequestCondition combine(HeadersRequestCondition other) {
        Set<HeaderExpression> set = new LinkedHashSet<>(this.expressions);
        set.addAll(other.expressions);
        return new HeadersRequestCondition(set);
    }

    /**
     * Returns "this" instance if the request matches all expressions;
     * or {@code null} otherwise.
     */
    @Override
    @Nullable
    public HeadersRequestCondition getMatchingCondition(HttpServletRequest request) {
        if (CorsUtils.isPreFlightRequest(request)) {
            return PRE_FLIGHT_MATCH;
        }
        for (HeaderExpression expression : expressions) {
            if (!expression.match(request)) {
                return null;
            }
        }
        return this;
    }

    /**
     * Returns:
     * <ul>
     * <li>0 if the two conditions have the same number of header expressions
     * <li>Less than 0 if "this" instance has more header expressions
     * <li>Greater than 0 if the "other" instance has more header expressions
     * </ul>
     * <p>It is assumed that both instances have been obtained via
     * {@link #getMatchingCondition(HttpServletRequest)} and each instance
     * contains the matching header expression only or is otherwise empty.
     */
    @Override
    public int compareTo(HeadersRequestCondition other, HttpServletRequest request) {
        return other.expressions.size() - this.expressions.size();
    }


    /**
     * Parses and matches a single header expression to a request.
     */
    static class HeaderExpression extends AbstractNameValueExpression<String> {

        public HeaderExpression(String expression) {
            super(expression);
        }

        @Override
        protected boolean isCaseSensitiveName() {
            return false;
        }

        @Override
        protected String parseValue(String valueExpression) {
            return valueExpression;
        }

        @Override
        protected boolean matchName(HttpServletRequest request) {
            return (request.getHeader(this.name) != null);
        }

        @Override
        protected boolean matchValue(HttpServletRequest request) {
            return ObjectUtils.nullSafeEquals(this.value, request.getHeader(this.name));
        }
    }

}
